Trithiophosphites of mercapto acid esters



United States Patent 3,374,291 TRITHIOPHOSPHITES F MERCAPTO AQID ESTERSHerbert Myers, Cherry Hill, N.J., assignor to Mobil Oil Corporation, acorporation of New York No Drawing. Filed May 25, 1964, Ser. No. 370,1126 Claims. (Cl. 260942) This invention relates to improved lubricatingcomposi tions. More particularly, it relates to a new type ofmultifunctional additive for such lubricants and a method for theirpreparation.

It is well known that lubricating compositions are susceptible tooxidation under various conditions of use. For example, oxidation isparticularly severe under the high temperature and pressure conditionsencountered in internal combustion engines. Such oxidation producesacidic bodies in the lubricating oil which are corrosive to the metalparts of the engine and further results in the deposition ofcarbonaceous sludge, lacquer and resinous materials whose accumulationimpairs the operating efficiency of the engine. In an effort toovercome, insofar as possible, these and other deleterious effects ofoxidation it has become the practice to add to the lubricants minoramounts of chemical agents which are commonly known as antioxidants.

It is also the practice to add ingredients to lubricating compositionsfor the purpose of improving their extreme pressure characteristics,particularly when these compositions are used for lubricating metalsurfaces which are subjected to extremely high pressures and highrubbing speeds such as exist in hypoid gears. Such high pressureconditions tend to disrupt the lubricating film with resulting damage tothe metal parts to be lubricated. Numerous additives commonly referredto as extreme pressure (E.P.) agents which act to improve the propertiesof the lubricant under these conditions, are known.

Ordinarily, a combination of antioxidants and BF. agents must beutilized in lubricating compositions in order to provide the desiredeffects.

The present invention, however, provides a new class of addition agentswhich are multi-functional in their activity, i.e., they are capable ofimproving lubricants in several respects and particularly with regard tooxidation stability and extreme pressure characteristics.

The additives of this invention may be characterized astrithiophosphites of mercapto acid esters. As far as is known, theseadditive compounds have not been prepared heretofore and they aretherefore considered to be new compositions of matter.

It is therefore an object of the present invention to provide certainnovel trithiophosphites of mercapto acid esters. A further object is toprovide improved lubricating compositions containing thesetrithiophosphites. Another object is to improve the characteristics,particularly the oxidation stability and BF. qualities of lubricants bythe addition thereto of such trithiophosphites. Other objects of theinvention and further advantages thereof will become apparent from thefollowing detailed description.

The trithiophosphites of mercapto acid esters of the present inventionmay be represented by the general formula,

R O (1)11RS]3 wherein R is a saturated or unsaturated aliphatic group,aryl group, substituted aliphatic or substituted aryl group containingsubstituents such as halogens, nitro, cyano, alkyl groups etc.; R is asaturated or unsaturated aliphatic or cycloaliphatic group, an arylgroup, or substituted aliphatic, cycloaliphatic or aryl group containingsuitable substituents, e.g., halogens, nitro, cyano, alkyl etc.; and nis an integer from 1 to 3 inclusive.

Some examples of suitable R groups include alkylene groups, such asmethylene, ethylene, propylene, butylene, etc.; halogenated alkylenegroups, such as chloroethylene; arylene groups or substituted arylenegroups, such as phenylene, naphthalene, or phenylene or naphthalenesubstituted by one or more substituents.

Some examples of suitable R groups include aliphatic groups, such asmethyl, ethyl, propyl, butyl, octyl, oleyl, octadecyl, etc.; substitutedaliphatics such as monoand poly-halogenated alkyls; aryl groups, such asphenyl and naphthyl; and substituted .aryls such as phenyl or naphthylssubstituted with one or more suitable substituents. In addition, R maybe a cycloaliphatic group, either unsubstituted or substituted, such ascyclobutyl, cyclopentyl, cyclohexyl, etc.

R preferably contains from 1 to about 40 carbon atoms, the greaternumber of carbons being generally present when n is more than one; whileR' may possess preferably from 1 to about 18 carbon atoms. It will benoted from the general formula that the phosphites may contain from oneto three carboxylic acid ester groups depending on the value of n.Compounds containing one or two carboxylic acid ester groups arepreferred.

The trithiophosphites of the invention may, in general, be prepared byreacting phosphorus trihalide (PX with a selected mercapto acid ester inthe presence of a suitable base such as tertiary amines, aqueous sodiumhydroxide, aqueous sodium carbonate, etc.

The reaction may be illustrated as follows:

0 3(R O )uRSH PXa -I- 3 Base wherein R, R and n have the meanings givenabove. Various amounts of mercapto acid ester and base may be employed.In general, however, the relative proportions are selected so as tosupply at least about 3 mols of base per mol of the phosphorustrihalide.

The reaction is desirably carried out in a non-polar solvent, such asbenzene, toluene, isooctane, etc. Although the reaction may be conductedat ambient temperatures, reaction temperatures in the range from about15 to 50 C. and reaction periods of from about 5 to 15 hours arepreferred. The products may be recovered by removing the precipitatedbase-hydrochloride, such as by filtration, washing the filtrate with 15%hydrochloric acid and water to remove unreacted base, and then toppingoff the non-polar solvent and unreac-ted mercapto acid ester.

Exemplary of the t-rithiophosphites of the invention are those obtainedfrom (a) aliphatic mono-carboxylic mercapto acid esters, and (b)aliphatic polycarboxylic mercapto acid esters and (c) aromaticcarboxylic mercapto esters according to the above reaction, andpossessing the formula:

[RO h (OHilxShP R'O(%(CH2)1 OHS P RO o oi-n)y 3 and where x and yrepresent integers from 1-18. As will be seen from Formula c, the sulfurof the trithiophosphites of the aromatic mercapto esters may be eitherortho, meta or para to the ca'rb-oxylic ester group. In addition, asindicated in the general formula, the aromatic ring of thesetrithiophosphites may also possess other groups, such as .a-lkyl,halogen, nit-r0, cyano, e-tc., attached thereto.

The following examples illustrate the preparation of some typicaltrit-hiophosphites of mercapto acid esters.

Example 1.Tritlziphosphite of butyl thi0glyc0latell P[SCH2C O Odin]:

Phosphorus trichloride (137 g., 1.0 mole) was added over a period of /2hour to a solution of butyl thioglycolate (450 g., 3.1 moles) andtriethylamine (312 g., 3.1 moles) in 3.0 liters of benzene whilemaintaining the reaction temperature at around C. Immediateprecipitation of triethyla-mine hydrochloride occurred. Nitrogen wasthen introduced and the slurry stirred at 15 to C. for 2 hours and at 50C. for an additional 3 hours.

The precipitated triethylamine hydrochloride was filtered off and washedwith one liter of benzene. Unreac'ted triethylamine was removed bywashing the filtrate with 250 ml. cold 15% hydrochloric acid and 4-500ml. portions of cold water. After drying the benzene solution overanhydrous potassium carbonate and sodium sulfate, the product wasisolated by topping to a pot temperature of 110 C. with nitrogen; to 130C. under 0.2 mm. pressure and finally filtering through diatomaceousearth.

The resulting product was a clear, pale yellow, viscous liquid whichanalyzed as follows Actual: P, 6.4%; S, 20.8%; C1, nil. Theoretical: P,6.5%; S, 20.3%; C1, nil.

Example 2.Trithiophosphite 0] octyl thi0glyc0late Following theprocedure of Example 1, phosphorus trichloride (68 g., 0.5 mole) wasreacted with octyl thioglycolate (350 g., 16 moles) and triethylamine(162 g., 1.6 moles) in 2.0 liters of benzene. The product was a viscous,clear pale yellow liquid which analyzed as follows' Actual: P, 4.6%; S,15.0%; C1, nil. Theoretical: P, 4.5%; S, 14.1%; Cl, nil.

Example 3.Trithiophosphife of Z-chloroethyl thiaglyc0la1te 0 llrtsotnooontomona Following the procedure of Example 1, phosphorustrichloride (48 g., 0.35 mole) was reacted with 2-chloroethylthioglycolate (180 g., 1.13 moles) and triethylamine (115 g., 1.13moles) in 2.0 liters of benzene. The product was a very viscous, clear,pale yellow liquid which analyzed as follows Actual: P, 6.0%; S, 21.1%;C1, 21.0%. Theoretical: P, 6.3%; S, 19.6%; C1, 21.7%.

Example 4.Trithi0ph0sphite of butyl thipropionateo P[SCH2CH2(JOC4H9]3Following the procedure of Example 1, phosphorus trichloride (137 g.,1.0 mole) was reacted with butyl thiopropionate (510 g., 3.15 moles) andtriethylamine (318 g., 3.15 moles) in 3.0 liters benzene. The productwas a pale yellow, clear, viscous liquid that had the following analysisActual: P, 5.8%; S, 19.3%; C1, nil. Theoretical: P, 6.0%; S, 18.7%; Cl,nil.

Example 5.Tr1'thi0ph0sphite of butyl thi0salzlcylate- Following theprocedure of Example 1, phosphorus trichloride (14 g., 0.10 mole) wasreacted with butyl thiosalicylate (69 g., 0.31 mole) and triethylamine(33 g., 0.33 mole) in 500 ml. benzene. The product was a pale yellow,waxy solid that had the following analysis Actual: P, 4.2%; S, 14.1%;Cl, nil. Theoretical: P, 4.7%; S, 14.6%; C1, nil.

Example 6.-Trithi0ph0sphite of dibutylthiomalonate o SCIIOC4H9 CH(3OC4HqFollowing the procedure of Example 1, phosphorus trichloride (89 g.,0.65 mole) was reacted with dibutylthiomalonate (521 g., 2.0 moles) andtriethyla'mine (202 g., 2.0 moles) in 2.0 liters benzene. The productwas a pale yellow, clear viscous liquid that gave the followinganalysis- Actual: P, 4.2%; S, 14.1%; C1, nil. Theoretical: P, 4.7%; S,14.6%; C1, nil.

CATALYTIC OXIDATION TEST In order to demonstrate the effectiveness ofthe compounds of this invention in inhibiting the catalytic oxidation ofoils, the trithiophosphites of the working examples were subjected to aCatalytic Oxidation Test. This test is based on the fact that theoxidized products which form in the oil are known to be acidic incharacter. Thus, the higher the neutralization number (N.N.), thegreater the extent of oxidation. The ability of a compound to maintainthe N.N. of an oil composition at a low level is a measure of itsantioxidant ability.

According to the test procedure, 25 ccs. of the test oil is placed in a200 x 25 mm. test tube with 15.6 sq. in. of sand-blasted iron wire, 0.78sq. in. of polished copper wire, 0.87 sq. in. of polished aluminum wireand 0.167 sq. in. of a polished lead surface. Dry air is passed throughthe sample at the rate of 10 liters per hour while heating in analuminum block bath for a period of 24 hours at a temperature of 325 F.The minimum concentration of phosphorus necessary to maintain theacidity of the oxidized oil below a neutralization number of 2 isdetermined and reported in the following Table I.

It will be seen from Table I that by employing the trithiophosphites ofthe invention less than 0.10% of phosphorus is required to maintain theneutralization number of the oil below 2.

TABLE L-GATALYTIC OXIDATION TEST Trithiophosphite Minimum percent ofExample Number Phosphorus l The base oil used was a SAE 10, solventrefined Mid-Continent oil SAE LOAD TEST in the same direction while agradually increasing load is mechanically applied. The machine isoperated at a TABLE IL-SAE LOAD TEST Trithiophosphite Phosphorus Cont.

of Example N o. (Wt. percent) SAE Load Test, 500 r.p.m. Seizure Load 1o. 5 460+, 460+ 2 0.5 460+, 460+ 3 o. 5 410, 460+ 4 o. 5 400, 415 5 0. 5390, 390

I The base oil used was a SAE 00, solvent refined, Mid-Continent Oil.

2 Fails break in. Break ln=20 pounds.

The trithiophosphites of this invention are effective in improving thecharacteristics particularly the oxidation stability and ERcharacteristics of a variety of lubricants including lubricating oils,greases, hydraulic fluids etc. These lubricants may contain eithermineral or synthetic base oils. Thus, mineral oils from various crudes,both solvent and acid refined, hydrocracked, etc., as well as synthetichydrocarbons, including olefin polymers, hydrogenated olefin polymers,alkyl benzenes, etc., synthetic esters, such as di-Z-ethylhexylsebacate, dialkyl adipate, trirnethylol propane dioctanoate, etc.,silicone fluids and the like may have their characteristics improved bythe addition of the trithiophosphites described herein.

The amount of trithiophosphite added to the lubricant Will depend onvarious factors, including the type of the lubricant the presence orabsence of other ingredients, the extent of oxidation stability desired,etc. In general, the trithiophosphites are employed in amounts fromabout 0.1 to about 10, preferably from about 0.5 to about 5 weightpercent.

The lubricating compositions of the present invention may, of course,also contain efiective quantities of various other materials which arenormally used therein such as detergents, inhibitors, V.I. improvers,thickening agents, defoamants, supplemental antioxidants or E.P. agents,etc.

It will, of course, be appreciated that many variations andmodifications may be practiced without departing from the scope andspirit of the present invention.

6 Having thus described the invention, what I desire to obtain andsecure by Letters Patent is:

1. A mercapto acid ester trithiophosphite of the formula 1? [(RO OhRSlaPwherein R is selected from the class consisting of alkylene, alkenylene,arylene, alkarylene and aralkylene having from 1 to about 40 carbonatoms; R is selected from the class consisting of alkyl, cycloalkyl,alkeny-l, aryl, alkaryl, aralkyl, and monochloroalkyl and having from 1to about 18 carbon atoms; and n is an integer of from 1 to 3, and when Ris alkyl, R is selected from the class consisting of alkenylene,arylene, alkary-lene and aralkylene.

2. A trithiophosphite according to claim 1 of the formula:

5 [RO k? (CH2) xSlaP where x is an integer from 1 to about 18 wherein Ris se lected from the class consisting of alkenyl, aryl, alkaryl,aralkyl and monochloro alkyl.

3. A trithiophosphite according to claim 1 of the formula:

R'OC S P 4. A trithiophosphite according to claim 1 of the formula:

0 R 0 g (0 H2) x 0 OHS R 0 A l (43112) y 3 where x and y are integersfrom 1 to about 18.

5. A trithiophosphite of 2-chloroethyl thioglycolate. 6. Atrithiophosphite of butyl thiosalicylate.

References Cited UNITED STATES PATENTS 2,824,847 2/1958 Fath 260-942 XCHARLES B. PARKER, Primary Examiner.

F. M. SIKORA, A. H. SUTTO, Assistant Examiners.

1. A MERCAPTO ACID ESTER TRITHIOPHOSPHITE OF THE FORMULA